Flash memory block retirement policy

ABSTRACT

Devices and techniques for a flash memory block retirement policy are disclosed herein. In an example embodiment, a first memory block is provisionally removed from service in response to encountering read errors in the first memory block. Memory pages of the first memory block are tested in a second mode comprising reading memory pages at different read voltages. A raw bit error rate (RBER) or a read window budget (RWB) is determined for memory pages at the different read voltages and the provisionally removed first memory block is returned to service or retired based on the determined RBER or the RWB.

PRIORITY APPLICATION

This application is a continuation of U.S. application Ser. No.16/504,067, filed Jul. 5, 2019, which is a continuation of U.S.application Ser. No. 15/690,903, filed Aug. 30, 2017, now issued as U.S.Pat. No. 10,387,281, each of which are incorporated herein by referencein their entireties.

BACKGROUND

Memory devices are typically provided as internal, semiconductor,integrated circuits in computers or other electronic devices. There aremany different types of memory, including volatile and non-volatilememory.

Volatile memory requires power to maintain its data, and includesrandom-access memory (RAM), dynamic random-access memory (DRAM), orsynchronous dynamic random-access memory (SDRAM), among others.

Non-volatile memory can retain stored data when not powered, andincludes flash memory, read-only memory (ROM), electrically erasableprogrammable ROM (EEPROM), static RAM (SRAM), erasable programmable ROM(EPROM), resistance variable memory, such as phase-change random-accessmemory (PCRAM), resistive random-access memory (RRAM), magnetoresistiverandom-access memory (MRAM), or 3D XPoint™ memory, among others.

Flash memory is utilized as non-volatile memory for a wide range ofelectronic applications. Flash memory devices typically include one ormore groups of one-transistor, floating gate or charge trap memory cellsthat allow for high memory densities, high reliability, and low powerconsumption.

Two common types of flash memory array architectures include NAND andNOR architectures, named after the logic form in which the basic memorycell configuration of each is arranged. The memory cells of the memoryarray are typically arranged in a matrix. In an example, the gates ofeach floating gate memory cell in a row of the array are coupled to anaccess line (e.g., a word line). In a NOR architecture, the drains ofeach memory cell in a column of the array are coupled to a data line(e.g., a bit line). In a NAND architecture, the drains of each memorycell in a string of the array are coupled together in series, source todrain, between a source line and a bit line.

Both NOR and NAND architecture semiconductor memory arrays are accessedthrough decoders that activate specific memory cells by selecting theword line coupled to their gates. In a NOR architecture semiconductormemory array, once activated, the selected memory cells place their datavalues on bit lines, causing different currents to flow depending on thestate at which a particular cell is programmed. In a NAND architecturesemiconductor memory array, a high bias voltage is applied to adrain-side select gate (SGD) line. Word lines coupled to the gates ofthe unselected memory cells of each group are driven at a specified passvoltage (e.g., Vpass) to operate the unselected memory cells of eachgroup as pass transistors (e.g., to pass current in a manner that isunrestricted by their stored data values). Current then flows from thesource line to the bit line through each series coupled group,restricted only by the selected memory cells of each group, placingcurrent encoded data values of selected memory cells on the bit lines.

Each flash memory cell in a NOR or NAND architecture semiconductormemory array can be programmed individually or collectively to one or anumber of programmed states. For example, a single-level cell (SLC) canrepresent one of two programmed states (e.g., 1 or 0), representing onebit of data.

However, flash memory cells can also represent one of more than twoprogrammed states, allowing the manufacture of higher density memorieswithout increasing the number of memory cells, as each cell canrepresent more than one binary digit (e.g., more than one bit). Suchcells can be referred to as multi-state memory cells, multi-digit cells,or multi-level cells (MLCs). In certain examples, MLC can refer to amemory cell that can store two bits of data per cell (e.g., one of fourprogrammed states), a triple-level cell (TLC) can refer to a memory cellthat can store three bits of data per cell (e.g., one of eightprogrammed states), and a quad-level cell (QLC) can store four bits ofdata per cell. MLC is used herein in its broader context, to can referto any memory cell that can store more than one bit of data per cell(i.e., that can represent more than two programmed states).

Traditional memory arrays are two-dimensional (2D) structures arrangedon a surface of a semiconductor substrate. To increase memory capacityfor a given area, and to decrease cost, the size of the individualmemory cells has decreased. However, there is a technological limit tothe reduction in size of the individual memory cells, and thus, to thememory density of 2D memory arrays. In response, three-dimensional (3D)memory structures such as 3D NAND architecture semiconductor memorydevices are being developed to further increase memory density and lowermemory cost.

Such 3D NAND devices often include strings of storage cells, coupled inseries (e.g., drain to source), between one or more source-side selectgates (SGSs) proximate a source, and one or more drain-side select gates(SGDs) proximate a bit line. In an example, the SGSs or the SGDs caninclude one or more field-effect transistors (FETs) or metal-oxidesemiconductor (MOS) structure devices, etc. In some examples, thestrings will extend vertically, through multiple vertically spaced tierscontaining respective word lines. A semiconductor structure (e.g., apolysilicon structure) may extend adjacent a string of storage cells toform a channel for the storages cells of the string. In the example of avertical string, the polysilicon structure may be in the form of avertically extending pillar. In some examples the string may be“folded,” and thus arranged relative to a U-shaped pillar. In otherexamples, multiple vertical structures may be stacked upon one anotherto form stacked arrays of storage cell strings.

Memory arrays or devices can be combined together to form a storagevolume of a memory system, such as a solid-state drive (SSD), aUniversal Flash Storage (UFS™) device, a MultiMediaCard (MMC)solid-state storage device, an embedded MMC device (eMMC™), etc. An SSDcan be used as, among other things, the main storage device of acomputer, having advantages over traditional hard drives with movingparts with respect to, for example, performance, size, weight,ruggedness, operating temperature range, and power consumption. Forexample, SSDs can have reduced seek time, latency, or other delayassociated with magnetic disk drives (e.g., electromechanical, etc.).SSDs use non-volatile memory cells, such as flash memory cells toobviate internal battery supply requirements, thus allowing the drive tobe more versatile and compact.

An SSD can include a number of memory devices, including a number ofdies or logical units (e.g., logical unit numbers or LUNs), and caninclude one or more processors or other controllers performing logicfunctions required to operate the memory devices or interface withexternal systems. Such SSDs may include one or more flash memory die,including a number of memory arrays and peripheral circuitry thereon.The flash memory arrays can include a number of blocks of memory cellsorganized into a number of physical pages. In many examples, the SSDswill also include DRAM or SRAM (or other forms of memory die or othermemory structures). The SSD can receive commands from a host inassociation with memory operations, such as read or write operations totransfer data (e.g., user data and associated integrity data, such aserror data and address data, etc.) between the memory devices and thehost, or erase operations to erase data from the memory devices.

Flash memory devices may exhibit data errors for a number of reasons.For example, a memory cell may fail to retain its previously programmedstate over some extended time period, such as when exposed to elevatedtemperatures. These types of errors are often called “data retention”errors, and are distinguished from other data retention errors in whicha number of program/erase (P/E) cycles has exceeded some expectedmaximum. In other cases, the state of a memory cell may be readincorrectly if the temperature of the memory cell is significantlydifferent from the temperature of the cell when it was programmed. Sucherrors are termed “cross-temperature” errors, which may occur when thecell temperature during a programming cycle is significantly higher orlower than the cell temperature during a subsequent reading cycle. Sucherrors may be more prevalent in changing and challenging environmentalconditions, such as those that may be encountered in mobile andautomotive applications, which may involve expansive operatingtemperature ranges.

Other errors may be produced when a memory cell is read, which may causethe threshold voltages of nearby memory cells to shift, possiblyaffecting the ability to read those nearby cells. Such “read disturb”errors have become more problematic as the density and speed of flashmemory devices have improved.

The above errors, as well as others not explicitly discussed herein, maybe viewed as intrinsic, as they typically occur as a result of variousconditions that may be expected during the use of the memory device. Incontrast, other memory cell errors, such as memory cell defects thatoccur during the manufacturing of the memory device, are more unexpectedor extrinsic in nature, and thus tend to be more permanent thanintrinsic errors.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

FIG. 1 illustrates an example of an environment including a memorydevice.

FIGS. 2-3 illustrate schematic diagrams of an example of a 3D NANDarchitecture semiconductor memory array.

FIG. 4 illustrates a block diagram of an example memory module.

FIG. 5 illustrates a flow diagram of an example method of implementing ablock retirement policy for a memory array.

FIG. 6 illustrates a flow diagram of an example method of testing amemory block in the example block retirement policy method of FIG. 5.

FIG. 7 is a block diagram illustrating an example of a machine uponwhich one or more embodiments may be implemented.

DETAILED DESCRIPTION

In at least some example embodiments described below, a memory block maybe tested to determine whether read errors exhibited by the memory blockare of a temporary or more permanent nature. If read errors encounteredin the memory block exceed a particular threshold or level, at leastsome of the data from the memory block may be stored elsewhere, and thememory block may be tested by erasing, programming, and reading thememory block a number of times to determine whether the read errors aremore temporary (and thus potentially mitigated during the testingprocess) or more permanent in origin. Based on that determination, thememory block may be returned to service or permanently retired. In someexample embodiments, a memory controller incorporated within the memorydevice containing the memory blocks may perform these operations, assuch a controller is likely to be configured to exercise more controlover one or more parameters of the erasing, programming, and readingprocesses of the memory device compared to a host device that employsthe memory device.

Electronic devices, such as mobile electronic devices (e.g., smartphones, tablets, etc.), electronic devices for use in automotiveapplications (e.g., automotive sensors, control units, driver-assistancesystems, passenger safety or comfort systems, etc.), andInternet-connected appliances or devices (e.g., internet-of-things (IoT)devices, etc.), have varying storage needs depending on, among otherthings, the type of electronic device, use environment, performanceexpectations, etc.

Electronic devices can be broken down into several main components: aprocessor (e.g., a central processing unit (CPU) or other mainprocessor); memory (e.g., one or more volatile or non-volatilerandom-access memory (RAM) memory device, such as dynamic RAM (DRAM)mobile or low-power double-data-rate synchronous DRAM (DDR SDRAM),etc.); and a storage device (e.g., non-volatile memory (NVM) device,such as flash memory, read-only memory (ROM), an SSD, an MMC, or othermemory card structure or assembly, etc.). In certain examples,electronic devices can include a user interface (e.g., a display,touch-screen, keyboard, one or more buttons, etc.), a graphicsprocessing unit (GPU), a power management circuit, a baseband processoror one or more transceiver circuits, etc.

FIG. 1 illustrates an example of an environment 100 including a hostdevice 105 and a memory device 110 configured to communicate over acommunication interface. The host device 105 or the memory device 110may be included in a variety of products 105, such as Internet of Things(IoT) devices (e.g., a refrigerator or other appliance, sensor, motor oractuator, mobile communication device, automobile, drone, etc.) tosupport processing, communications, or control of the product 150.

The memory device 110 includes a memory controller 115 and a memoryarray 120 including, for example, a number of individual memory die(e.g., a stack of three-dimensional (3D) NAND die). In 3D architecturesemiconductor memory technology, vertical structures are stacked,increasing the number of tiers, physical pages, and accordingly, thedensity of a memory device (e.g., a storage device). In an example, thememory device 110 can be a discrete memory or storage device componentof the host device 105. In other examples, the memory device 110 can bea portion of an integrated circuit (e.g., system on a chip (SOC), etc.),stacked or otherwise included with one or more other components of thehost device 105.

One or more communication interfaces can be used to transfer databetween the memory device 110 and one or more other components of thehost device 105, such as a Serial Advanced Technology Attachment (SATA)interface, a Peripheral Component Interconnect Express (PCIe) interface,a Universal Serial Bus (USB) interface, a Universal Flash Storage (UFS)interface, an eMMC™ interface, or one or more other connectors orinterfaces. The host device 105 can include a host system an electronicdevice, a processor, a memory card reader, or one or more otherelectronic devices external to the memory device 110. In some examples,the host 105 may be a machine having some portion, or all, of thecomponents discussed in reference to the machine 500 of FIG. 5.

The memory controller 115 can receive instructions from the host 105,and can communicate with the memory array, such as to transfer data to(e.g., write or erase) or from (e.g., read) one or more of the memorycells, planes, sub-blocks, blocks, or pages of the memory array. Thememory controller 115 can include, among other things, circuitry orfirmware, including one or more components or integrated circuits. Forexample, the memory controller 115 can include one or more memorycontrol units, circuits, or components configured to control accessacross the memory array 120 and to provide a translation layer betweenthe host 105 and the memory device 110. The memory controller 115 caninclude one or more input/output (I/O) circuits, lines, or interfaces totransfer data to or from the memory array 120. The memory controller 115can include a memory manager 125 and an array controller 135.

The memory manager 125 can include, among other things, circuitry orfirmware, such as a number of components or integrated circuitsassociated with various memory management functions. For purposes of thepresent description example memory operation and management functionswill be described in the context of NAND memory. Persons skilled in theart will recognize that other forms of non-volatile memory may haveanalogous memory operations or management functions. Such NANDmanagement functions include wear leveling (e.g., garbage collection orreclamation), error detection or correction, block retirement, or one ormore other memory management functions. The memory manager 125 can parseor format host commands (e.g., commands received from a host) intodevice commands (e.g., commands associated with operation of a memoryarray, etc.), or generate device commands (e.g., to accomplish variousmemory management functions) for the array controller 135 or one or moreother components of the memory device 110.

The memory manager 125 can include a set of management tables 130configured to maintain various information associated with one or morecomponent of the memory device 110 (e.g., various information associatedwith a memory array or one or more memory cells coupled to the memorycontroller 115). For example, the management tables 130 can includeinformation regarding block age, block erase count, error history, orone or more error counts (e.g., a write operation error count, a readbit error count, a read operation error count, an erase error count,etc.) for one or more blocks of memory cells coupled to the memorycontroller 115. In certain examples, if the number of detected errorsfor one or more of the error counts is above a threshold, the bit errorcan be referred to as an uncorrectable bit error. The management tables130 can maintain a count of correctable or uncorrectable bit errors,among other things.

The array controller 135 can include, among other things, circuitry orcomponents configured to control memory operations associated withwriting data to, reading data from, or erasing one or more memory cellsof the memory device 110 coupled to the memory controller 115. Thememory operations can be based on, for example, host commands receivedfrom the host 105, or internally generated by the memory manager 125(e.g., in association with wear leveling, error detection or correction,etc.).

The array controller 135 can include an error correction code (ECC)component 140, which can include, among other things, an ECC engine orother circuitry configured to detect or correct errors associated withwriting data to or reading data from one or more memory cells of thememory device 110 coupled to the memory controller 115. The memorycontroller 115 can be configured to actively detect and recover fromerror occurrences (e.g., bit errors, operation errors, etc.) associatedwith various operations or storage of data, while maintaining integrityof the data transferred between the host 105 and the memory device 110,or maintaining integrity of stored data (e.g., using redundant RAIDstorage, etc.), and can remove (e.g., retire) failing memory resources(e.g., memory cells, memory arrays, pages, blocks, etc.) to preventfuture errors.

The memory array 120 can include several memory cells arranged in, forexample, a number of devices, planes, sub-blocks, blocks, or pages. Asone example, a 48 GB TLC NAND memory device can include 18,592 bytes (B)of data per page (16,384+2208 bytes), 1536 pages per block, 548 blocksper plane, and 4 or more planes per device. As another example, a 32 GBMLC memory device (storing two bits of data per cell (i.e., 4programmable states)) can include 18,592 bytes (B) of data per page(16,384+2208 bytes), 1024 pages per block, 548 blocks per plane, and 4planes per device, but with half the required write time and twice theprogram/erase (P/E) cycles as a corresponding TLC memory device. Otherexamples can include other numbers or arrangements. In some examples, amemory device, or a portion thereof, may be selectively operated in SLCmode, or in a desired MLC mode (such as TLC, QLC, etc.).

In operation, data is typically written to or read from the NAND memorydevice 110 in pages, and erased in blocks. However, one or more memoryoperations (e.g., read, write, erase, etc.) can be performed on largeror smaller groups of memory cells, as desired. The data transfer size ofa NAND memory device 110 is typically referred to as a page, whereas thedata transfer size of a host is typically referred to as a sector.

Although a page of data can include a number of bytes of user data(e.g., a data payload including a number of sectors of data) and itscorresponding metadata, the size of the page often refers only to thenumber of bytes used to store the user data. As an example a page ofdata having a page size of 4 KB may include 4 KB of user data (e.g., 8sectors assuming a sector size of 512 B) as well as a number of bytes(e.g., 32 B, 54 B, 224 B, etc.) of metadata corresponding to the userdata, such as integrity data (e.g., error detecting or correcting codedata), address data (e.g., logical address data, etc.), or othermetadata associated with the user data.

Different types of memory cells or memory arrays 120 can provide fordifferent page sizes, or may require different amounts of metadataassociated therewith. For example, different memory device types mayhave different bit error rates, which can lead to different amounts ofmetadata necessary to ensure integrity of the page of data (e.g., amemory device with a higher bit error rate may require more bytes oferror correction code data than a memory device with a lower bit errorrate). As an example, a multilevel cell (MLC) NAND flash device may havea higher bit error rate than a corresponding single-level cell (SLC)NAND flash device. As such, the MLC device may require more metadatabytes for error data than the corresponding SLC device.

FIG. 2 illustrates an example schematic diagram of a 3D NANDarchitecture semiconductor memory array 200 including a number ofstrings of memory cells (e.g., first-third A₀ memory strings205A₀-207A₀, first-third A_(n) memory strings 205A_(n)-207A_(n),first-third B₀ memory strings 205B₀-207B₀, first-third B_(n) memorystrings 205B_(n)-207B_(n), etc.), organized in blocks (e.g., block A_(n)201A_(n), block B 201B, etc.) and sub-blocks (e.g., sub-block A₀ 201A₀,sub-block A_(n) 201A_(n), sub-block B₀ 201B₀, sub-block B_(n) 201B_(n),etc.). The memory array 200 represents a portion of a greater number ofsimilar structures that would typically be found in a block, device, orother unit of a memory device.

Each string of memory cells includes a number of tiers of charge storagetransistors (e.g., floating gate transistors, charge-trappingstructures, etc.) stacked in the Z direction, source to drain, between asource line (SRC) 235 or a source-side select gate (SGS) (e.g.,first-third A₀ SGS 231A₀-233A₀, first-third A_(n) SGS 231A_(n)-233A_(n),first-third B₀ SGS 231B₀-233B₀, first-third B_(n) SGS 231B_(n)-233B_(n),etc.) and a drain-side select gate (SGD) (e.g., first-third A₀ SGD226A₀-228A₀, first-third A_(n) SGD 226A_(n)-228A_(n), first-third B₀ SGD226B₀-228B₀, first-third B_(n) SGD 226B_(n)-228B_(n), etc.). Each stringof memory cells in the 3D memory array can be arranged along the Xdirection as data lines (e.g., bit lines (BL) BL0-BL2 220-222), andalong the Y direction as physical pages.

Within a physical page, each tier represents a row of memory cells, andeach string of memory cells represents a column. A sub-block can includeone or more physical pages. A block can include a number of sub-blocks(or physical pages) (e.g., 128, 256, 384, etc.). Although illustratedherein as having two blocks, each block having two sub-blocks, eachsub-block having a single physical page, each physical page having threestrings of memory cells, and each string having 8 tiers of memory cells,in other examples, the memory array 200 can include more or fewerblocks, sub-blocks, physical pages, strings of memory cells, memorycells, or tiers. For example, each string of memory cells can includemore or fewer tiers (e.g., 16, 32, 64, 128, etc.), as well as one ormore additional tiers of semiconductor material above or below thecharge storage transistors (e.g., select gates, data lines, etc.), asdesired. As an example, a 48 GB TLC NAND memory device can include18,592 bytes (B) of data per page (16,384+2208 bytes), 1536 pages perblock, 548 blocks per plane, and 4 or more planes per device.

Each memory cell in the memory array 200 includes a control gate (CG)coupled to (e.g., electrically or otherwise operatively connected to) anaccess line (e.g., word lines (WL) WL0 ₀-WL7 ₀ 210A-217A, WL0 ₁-WL7 ₁210B-217B, etc.), which collectively couples the control gates (CGs)across a specific tier, or a portion of a tier, as desired. Specifictiers in the 3D memory array, and accordingly, specific memory cells ina string, can be accessed or controlled using respective access lines.Groups of select gates can be accessed using various select lines. Forexample, first-third A₀ SGD 226A₀-228A₀ can be accessed using an A₀ SGDline SGDA₀ 225A₀, first-third A_(n) SGD 226A_(n)-228A_(n) can beaccessed using an A_(n) SGD line SGDA_(n) 225A_(n), first-third B₀ SGD226B₀-228B₀ can be accessed using an B₀ SGD line SGDB₀ 225B₀, andfirst-third B_(n) SGD 226B_(n)-228B_(n) can be accessed using an B_(n)SGD line SGDB_(n) 225B_(n). First-third A₀ SGS 231A₀-233A₀ andfirst-third A_(n) SGS 231A_(n)-233A_(n) can be accessed using a gateselect line SGS₀ 230A, and first-third B₀ SGS 231B₀-233B₀ andfirst-third B_(n) SGS 231B_(n)-233B_(n) can be accessed using a gateselect line SGS₁ 230B.

In an example, the memory array 200 can include a number of levels ofsemiconductor material (e.g., polysilicon, etc.) configured to couplethe control gates (CGs) of each memory cell or select gate (or a portionof the CGs or select gates) of a respective tier of the array. Specificstrings of memory cells in the array can be accessed, selected, orcontrolled using a combination of bit lines (BLs) and select gates,etc., and specific memory cells at one or more tiers in the specificstrings can be accessed, selected, or controlled using one or moreaccess lines (e.g., word lines).

FIG. 3 illustrates an example schematic diagram of a portion of a NANDarchitecture semiconductor memory array 300 including a plurality ofmemory cells 302 arranged in a two-dimensional array of strings (e.g.,first-third strings 305-307) and tiers (e.g., illustrated as respectiveword lines (WL) WL0-WL7 310-317, a drain-side select gate (SGD) line325, a source-side select gate (SGS) line 330, etc.), and senseamplifiers or devices 360. For example, the memory array 300 canillustrate an example schematic diagram of a portion of one physicalpage of memory cells of a 3D NAND architecture semiconductor memorydevice, such as illustrated in FIG. 2.

Each string of memory cells is coupled to a source line (SRC) using arespective source-side select gate (SGS) (e.g., first-third SGS331-333), and to a respective data line (e.g., first-third bit lines(BL) BL0-BL2 320-322) using a respective drain-side select gate (SGD)(e.g., first-third SGD 326-328). Although illustrated with 8 tiers(e.g., using word lines (WL) WL0-WL7 310-317) and three data lines(BL0-BL2 326-328) in the example of FIG. 3, other examples can includestrings of memory cells having more or fewer tiers or data lines, asdesired.

In a NAND architecture semiconductor memory array, such as the examplememory array 300, the state of a selected memory cell 302 can beaccessed by sensing a current or voltage variation associated with aparticular data line containing the selected memory cell. The memoryarray 300 can be accessed (e.g., by a control circuit, one or moreprocessors, digital logic, etc.) using one or more drivers. In anexample, one or more drivers can activate a specific memory cell, or setof memory cells, by driving a particular potential to one or more datalines (e.g., bit lines BL0-BL2), access lines (e.g., word linesWL0-WL7), or select gates, depending on the type of operation desired tobe performed on the specific memory cell or set of memory cells.

To program or write data to a memory cell, a programming voltage (Vpgm)(e.g., one or more programming pulses, etc.) can be applied to selectedword lines (e.g., WL4), and thus, to a control gate of each memory cellcoupled to the selected word lines (e.g., first-third control gates(CGs) 341-343 of the memory cells coupled to WL4). Programming pulsescan begin, for example, at or near 15V, and, in certain examples canincrease in magnitude during each programming pulse application. Whilethe program voltage is applied to the selected word lines, a potential,such as a ground potential (e.g., Vss), can be applied to the data lines(e.g., bit lines) and substrates (and thus the channels, between thesources and drains) of the memory cells targeted for programming,resulting in a charge transfer (e.g., direct injection orFowler-Nordheim (FN) tunneling, etc.) from the channels to the floatinggates of the targeted memory cells.

In contrast, a pass voltage (Vpass) can be applied to one or more wordlines having memory cells that are not targeted for programming, or aninhibit voltage (e.g., Vcc) can be applied to data lines (e.g., bitlines) having memory cells that are not targeted for programming, forexample, to inhibit charge from being transferred from the channels tothe floating gates of such non-targeted memory cells. The pass voltagecan be variable, depending, for example, on the proximity of the appliedpass voltages to a word line targeted for programming. The inhibitvoltage can include a supply voltage (Vcc), such as a voltage from anexternal source or supply (e.g., a battery, an AC-to-DC converter,etc.), relative to a ground potential (e.g., Vss).

As an example, if a programming voltage (e.g., 15V or more) is appliedto a specific word line, such as WL4, a pass voltage of 10V can beapplied to one or more other word lines, such as WL3, WL5, etc., toinhibit programming of non-targeted memory cells, or to retain thevalues stored on such memory cells not targeted for programming. As thedistance between an applied program voltage and the non-targeted memorycells increases, the pass voltage required to refrain from programmingthe non-targeted memory cells can decrease. For example, where aprogramming voltage of 15V is applied to WL4, a pass voltage of 10V canbe applied to WL3 and WL5, a pass voltage of 8V can be applied to WL2and WL6, a pass voltage of 7V can be applied to WL1 and WL7, etc. Inother examples, the pass voltages, or number of word lines, etc., can behigher or lower, or more or less.

The sense amplifiers 360, coupled to one or more of the data lines(e.g., first, second, or third bit lines (BL0-BL2) 320-322), can detectthe state of each memory cell in respective data lines by sensing avoltage or current on a particular data line.

Between applications of one or more programming pulses (e.g., Vpgm), averify operation can be performed to determine if a selected memory cellhas reached its intended programmed state. If the selected memory cellhas reached its intended programmed state, it can be inhibited fromfurther programming. If the selected memory cell has not reached itsintended programmed state, additional programming pulses can be applied.If the selected memory cell has not reached its intended programmedstate after a particular number of programming pulses (e.g., a maximumnumber), the selected memory cell, or a string, block, or pageassociated with such selected memory cell, can be marked as defective.

To erase a memory cell or a group of memory cells (e.g., erasure istypically performed in blocks or sub-blocks), an erasure voltage (Vers)(e.g., typically Vpgm) can be applied to the substrates (and thus thechannels, between the sources and drains) of the memory cells targetedfor erasure (e.g., using one or more bit lines select gates, etc.) whilethe word lines of the targeted memory cells are kept at a potential,such as a ground potential (e.g., Vss), resulting in a charge transfer(e.g., direct injection or Fowler-Nordheim (FN) tunneling, etc.) fromthe floating gates of the targeted memory cells to the channels.

FIG. 4 illustrates an example block diagram of a memory device 400including a memory array 402 having a plurality of memory cells 404, andone or more circuits or components to provide communication with, orperform one or more memory operations on, the memory array 402. Thememory device 400 can include a row decoder 412, a column decoder 414,sense amplifiers 420, a page buffer 422, a selector 424 an input/output(I/O) circuit 426, and a memory control unit 430.

The memory cells 404 of the memory array 402 can be arranged in blocks,such as first and second blocks 402A, 402B. Each block can includesub-blocks. For example, the first block 402A can include first andsecond sub-blocks 402A₀, 402A_(n), and the second block 402B can includefirst and second sub-blocks 402B₀, 402B_(n). Each sub-block can includea number of physical pages, each page including a number of memory cells404. Although illustrated herein as having two blocks, each block havingtwo sub-blocks, and each sub-block having a number of memory cells 404,in other examples, the memory array 402 can include more or fewerblocks, sub-blocks, memory cells, etc. In other examples, the memorycells 404 can be arranged in a number of rows, columns, pages,sub-blocks, blocks, etc., and accessed using, for example, access lines406, first data lines 410, or one or more select gates, source lines,etc.

The memory control unit 430 can control memory operations of the memorydevice 400 according to one or more signals or instructions received oncontrol lines 432, including, for example, one or more clock signals orcontrol signals that indicate a desired operation (e.g., write, read,erase, etc.), or address signals (A0-AX) received on one or more addresslines 416. One or more devices external to the memory device 400 cancontrol the values of the control signals on the control lines 432, orthe address signals on the address line 416. Examples of devicesexternal to the memory device 400 can include, but are not limited to, ahost, a memory controller, a processor, or one or more circuits orcomponents not illustrated in FIG. 4.

The memory device 400 can use access lines 406 and first data lines 410to transfer data to (e.g., write or erase) or from (e.g., read) one ormore of the memory cells 404. The row decoder 412 and the column decoder414 can receive and decode the address signals (AD-AX) from the addressline 416, can determine which of the memory cells 404 are to beaccessed, and can provide signals to one or more of the access lines 406(e.g., one or more of a plurality of word lines (WL0-WLm)) or the firstdata lines 410 (e.g., one or more of a plurality of bit lines(BL0-BLn)), such as described above.

The memory device 400 can include sense circuitry, such as the senseamplifiers 420, configured to determine the values of data on (e.g.,read), or to determine the values of data to be written to, the memorycells 404 using the first data lines 410. For example, in a selectedstring of memory cells 404, one or more of the sense amplifiers 420 canread a logic level in the selected memory cell 404 in response to a readcurrent flowing in the memory array 402 through the selected string tothe data lines 410.

One or more devices external to the memory device 400 can communicatewith the memory device 400 using the I/O lines (DQ0-DQN) 408, addresslines 416 (A0-AX), or control lines 432. The input/output (I/O) circuit426 can transfer values of data in or out of the memory device 400, suchas in or out of the page buffer 422 or the memory array 402, using theI/O lines 408, according to, for example, the control lines 432 andaddress lines 416. The page buffer 422 can store data received from theone or more devices external to the memory device 400 before the data isprogrammed into relevant portions of the memory array 402, or can storedata read from the memory array 402 before the data is transmitted tothe one or more devices external to the memory device 400.

The column decoder 414 can receive and decode address signals (A0-AX)into one or more column select signals (CSEL1-CSELn). The selector 424(e.g., a select circuit) can receive the column select signals(CSEL1-CSELn) and select data in the page buffer 422 representing valuesof data to be read from or to be programmed into memory cells 404.Selected data can be transferred between the page buffer 422 and the I/Ocircuit 426 using second data lines 418.

The memory control unit 430 can receive positive and negative supplysignals, such as a supply voltage (Vcc) 434 and a negative supply (Vss)436 (e.g., a ground potential), from an external source or supply (e.g.,an internal or external battery, an AC-to-DC converter, etc.). Incertain examples, the memory control unit 430 can include a regulator428 to internally provide positive or negative supply signals.

FIG. 5 illustrates a flow diagram of an example method 500 ofimplementing a block retirement policy for a memory array (e.g., thememory array 120). In the example embodiments described below, thememory array 120 is a NAND flash memory array, as discussed in detailabove. However, the method 500, as well as other methods described belowmay be applied to other memory arrays, devices, or systems.

In example embodiments in which a NAND flash memory array is used, themethod 500 may be performed by the memory controller 115 by way ofoperations performed in either or both of the memory manager 125 and thearray controller 135 of the memory device 110, and/or by the memorycontrol unit 430 of the memory device 400. Other modules or structuresother than those specifically described herein may perform the method500 and others described below in other example embodiments.

In example embodiments of the method 500, a first memory block (e.g.,memory block 201, 402) is read (operation 502), and a determination ismade as to whether one or more read errors are encountered that exceed afirst error threshold (operation 504). In some example embodiments, theoperation 502 is initiated by way of a read command (or similar command)received by the memory controller 115 from a host 105. In other exampleembodiments, the operation 502 may be initiated by the memory controller115 or another unit within a memory device (e.g., memory device 110,400). For example, the memory controller 115 may perform the operation502 as part of a memory “scrubbing” process, in which the memorycontroller 115 may read memory blocks that were previously written todetermine if read errors discovered in those memory blocks exceed somethreshold, and if so, possibly erase and rewrite those memory blocks toreduce the number of read errors encountered during subsequent readoperations. In some example embodiments, the memory controller 115 mayperform one or more error handling techniques, such as varying the readvoltage (e.g., the control gate (CG) voltages) of one or more memorycells of the first memory block, retrying the read operation multipletimes and the like, to recover the data.

Also in the method 500, if the number of read errors does not exceed thefirst error threshold, the remaining operations of the method 500 may beobviated, as the first memory block may be deemed to be possess anacceptable number of read errors. If, instead, the number of read errorsexceeds the first error threshold, processing of the first memory blockproceeds, as described below. In an example embodiment, the first errorthreshold is an error threshold or level at which all of the errors inthe memory block are correctable. In another example embodiment, thefirst error threshold is an error threshold or level at which at leastone of the errors in the first memory block is uncorrectable. In exampleembodiments, whether the read errors in the first memory block arecorrectable or uncorrectable may be determined using the ECC component140 of the array controller 135, as discussed above.

Presuming the number of read errors exceeds the first error threshold,the memory controller 115 (e.g., using the memory manager 125) may copydata that is recoverable (e.g., correctable) from the first memory blockto a second memory block (e.g., memory block 201, 402) (operation 506).For example, if all of the data of the first memory block arecorrectable, then all of the data may be copied to the second memoryblock. If less than all of the data of the first memory block arecorrectable, then only those portions of data that are correctable(e.g., data in less than all pages of the first memory block) may becopied to the second memory block. In other example embodiments, all ofthe data of the first memory block may be copied to the second memoryblock, even if some of the data is uncorrectable. Such information maybe tracked by way of the management tables 130 of the memory manager135, in some example embodiments.

In an example embodiment, the memory manager 125 may retrieve the secondmemory block from a “free pool” of memory blocks (e.g., a pool or groupof memory blocks that are currently unassigned for access by the host105) prior to the copying of the recoverable data from the first memoryblock to the second memory block. Also in example embodiments, thememory manager 125 may temporarily or provisionally retire, or otherwiseremove from service, the first memory block (operation 508), thuspreventing access to the first memory block by the host 105.

After the copying of the recoverable data from the first memory block(operation 506) and the removing of the first memory block from service(operation 508), the array controller 135 may iteratively test the firstmemory block (operation 510) to determine whether the first memory blockshould be retired (operation 512). In example embodiments described ingreater detail below, the array controller 135 may determine whether anyof the pages of the first memory block exhibited a number of read errorsexceeding a second error threshold during the testing (operation 512).An example of at least a portion of a page of the first memory block isdepicted in FIG. 3, as described above. Some example embodiments of theiterative testing of the first memory block are described below inconjunction with FIG. 6. In an example embodiment the second errorthreshold may be an error threshold at which all the read errors arecorrectable. In various example embodiments, the second error thresholdmay be the same as, or different from, the first error threshold.

If none of the pages of the first memory block exhibit a number of readerrors exceeding the second error threshold, the memory controller 115(e.g., using the memory manager 125) may make the memory block availablefor use (operation 514), such as by returning the first memory block 514to the free pool. If, instead, one or more of the pages of the firstmemory block exhibit a number of read errors exceeding the second errorthreshold, the memory controller 115 may permanently retire the firstmemory block (operation 516), thus preventing use of the first memoryblock by the host 105.

While the operations 502-516 are presented in a particular order in FIG.5, other orders of execution of the operations 502-516 may be possible,including simultaneous, concurrent, or overlapping execution of two ormore of the operations 502-516. For example, the copying of the datafrom the first memory block to the second memory block (operation 506)may occur after, or in concurrence with, the removing of the firstmemory block from service (operation 508).

In an example embodiment, the operations 506 through 516 of FIG. 5 maybe performed as background operations, or while the memory device 110 isoperating in a background mode during which the memory device 110 doesnot process access requests to the memory array 120 from the host 105.For example, in an example embodiment in which the memory device 110supports the eMMC™ standard, the operation 506 through 516 may beperformed as background operations (BKOPS).

FIG. 6 illustrates a flow diagram of an example method 600 of testing amemory block in the example block retirement policy method 500 of FIG.5. In an example embodiment, operations 602 through 614 of FIG. 6 serveas an example of the iterative testing of the first memory block (e.g.,memory block 201, 402) (operation 510 of FIG. 5).

In the method 600, at the start of each of one or more iterations, timemory controller 115 (e.g., via the array controller 135) may cause thefirst memory block to be erased (operation 602) and then programmed orwritten (operation 604). In some example embodiments, the erasure of thefirst memory block is accomplished as a single, block-level erasure.Also in example embodiments, while each byte, word, or other separatelyaddressable location of the first memory block may carry individualdata, the actual writing operation may occur on a page-by-page basis, oreven on a block-wide basis. Writing of data may occur in otherincrements of the first memory block in other example embodiments. Asindicated above, the writing of a page of the first memory block mayalso include the writing of ECC data to facilitate the reading andassociated correction of bit errors associated with that page.

In an example embodiment, the data written to each page of the firstmemory block may take any number of forms. For example, since an erasureof data may result in that data being read as all ones, the data writtento each page may be all zeros, alternating ones and zeros, or any otherpattern. Also in some example embodiments, the data written to each pagemay vary from iteration to iteration.

During each iteration, after the programming of the first memory block604 (operation 604), the array controller 135 may each page of the firstmemory block (operation 606), and the ECC code stored with that page maybe employed to correct bit errors in the read data (e.g., using the KCcomponent 140). In one example embodiment, the page may be read onceusing a nominal or default read voltage (e.g., a control gate (CG)voltage) normally expected to provide significant voltage thresholdmargin to render the lowest raw bit error rate (RBER). In other exampleembodiments, the page may employ an enhanced read mode, during whicheach page may be read one or more times during each iteration using oneor more different read voltages. For example, the page may be readseveral times each using a different read voltage about some nominal ordefault read voltage level so that a particular read voltage thatprovides the greatest read window budget (RWB), and thus the lowestRBER, may be used in determining whether the first memory block shouldbe retired or retained.

Based on the reading of each page, the memory controller 115, by way ofthe array controller 135 and the KC component 140, may determine whetherthe read errors of each pages exceeds the second error threshold(operation 608). In an example embodiment in which each page is readonly once during an iteration, the memory controller 115 may determinethat the read errors of a page exceed the second error threshold duringthat single read operation. In example embodiments, in which each pageis read multiple times, such as by using one or more read voltages, thememory controller 115 may determine that the read errors of a pageexceed the second error threshold if the second error threshold isexceeded for every read operation during a particular iteration. Such anexample may help prevent an over-retirement of memory blocks (sometimestermed “overkill”) that needlessly limits the number of memory blocksavailable for use by the host 105. In other examples, the memorycontroller 115 may determine that the read errors of a page exceed thesecond error threshold if the second error threshold is exceeded duringat least some minimum number of read operations during a particulariteration, such as one, two, and so on.

Based on a determination that at least one page of the first memoryblock contains read errors that exceed the second error threshold duringthe current iteration, the memory controller 115 may determine that thefirst memory block is to be permanently retired (operation 610) andproceed to operation 512 of FIG. 5. Otherwise, based on a determinationthat no page of the first memory block contained read errors that exceedthe second error threshold, the memory controller 115 may then determinewhether any more iterations are to be performed (operation 612). If so,the memory controller 115 may proceed with erasing (operation 602) andprogramming (operation 604) the first memory block, and continuing asdescribed above. Otherwise, if no more iterations remain to beperformed, the memory controller 115 may determine the first memoryblock is ready for service (operation 614). In some example embodiments,the memory controller 115 may also erase the first memory block oncemore before proceeding to operation 512 of method 500 of FIG. 5. Anynumber of iterations (e.g., one, two, five, ten, etc.) may be employedin the method 600 of FIG. 6.

Thus, by employing at least some of the example embodiments describedabove, a memory block that exhibits read errors of a particular levelmay be removed from service (at least temporarily) and tested, such asduring a background operational mode. Based on that testing, adetermination may be made as to whether the read errors are more likelyextrinsic and thus not likely to be remedied) or intrinsic (andtherefore not representative of a permanent or chronic failure mode).Correspondingly, memory blocks with primarily intrinsic errors may berehabilitated (e.g., via erasure) and returned to active service, whilememory blocks with primarily extrinsic errors may be permanently retiredto increase the overall RBER and performance level of the memory device110. Such example embodiments may especially benefit memory devicesemployed in demanding environmental conditions, such as those oftenencountered in mobile and automotive applications by distinguishingbetween those read errors that may be a temporary result of a particularoperating environment from those that may be more chronic.

FIG. 7 illustrates a block diagram of an example machine 700 upon whichany one or more of the techniques (e.g., methodologies) discussed hereinmay perform. In alternative embodiments, the machine 700 may operate asa standalone device or may be connected (e.g., networked) to othermachines. In a networked deployment, the machine 700 may operate in thecapacity of a server machine, a client machine, or both in server-clientnetwork environments. In an example, the machine 700 may act as a peermachine in peer-to-peer (P2P) (or other distributed) networkenvironment. The machine 700 may be a personal computer (PC), a tabletPC, a set-top box (STB), a personal digital assistant (PDA), a mobiletelephone, a web appliance, an IoT device automotive system, or anymachine capable of executing instructions (sequential or otherwise) thatspecify actions to be taken by that machine. Further, while only asingle machine is illustrated, the term “machine” shall also be taken toinclude any collection of machines that individually or jointly executea set (or multiple sets) of instructions to perform any one or more ofthe methodologies discussed herein, such as cloud computing, software asa service (SaaS), other computer cluster configurations.

Examples, as described herein, may include, or may operate by, logic,components, devices, packages, or mechanisms. Circuitry is a collection(e.g., set) of circuits implemented in tangible entities that includehardware (e.g., simple circuits, gates, logic, etc.). Circuitrymembership may be flexible over time and underlying hardwarevariability. Circuitries include members that may, alone or incombination, perform specific tasks when operating. In an example,hardware of the circuitry may be immutably designed to carry out aspecific operation (e.g., hardwired). In an example, the hardware of thecircuitry may include variably connected physical components (e.g.,execution units, transistors, simple circuits, etc.) including acomputer readable medium physically modified (e.g., magnetically,electrically, moveable placement of invariant massed particles, etc.) toencode instructions of the specific operation. In connecting thephysical components, the underlying electrical properties of a hardwareconstituent are changed, for example, from an insulator to a conductoror vice versa. The instructions enable participating hardware (e.g., theexecution units or a loading mechanism) to create members of thecircuitry in hardware via the variable connections to carry out portionsof the specific tasks when in operation. Accordingly, the computerreadable medium is communicatively coupled to the other components ofthe circuitry when the device is operating. In an example, any of thephysical components may be used in more than one member of more than onecircuitry. For example, under operation, execution units may be used ina first circuit of a first circuitry at one point in time and reused bya second circuit in the first circuitry, or by a third circuit in asecond circuitry at a different time.

The machine (e.g., computer system) 700 may include a hardware processor702 (e.g., a central processing unit (CPU), a graphics processing unit(GPU), a hardware processor core, or any combination thereof), a mainmemory 704 and a static memory 706, some or all of which may communicatewith each other via an interlink (e.g., bus) 708. The machine 700 mayfurther include a display unit 710, an alphanumeric input device 712(e.g., a keyboard), and a user interface (UI) navigation device 714(e.g., a mouse). In an example, the display unit 710, input device 712and UI navigation device 714 may be a touch screen display. The machine700 may additionally include a storage device (e.g., drive unit) 716, asignal generation device 718 (e.g., a speaker), a network interfacedevice 720 and one or more sensors 716 such as a global positioningsystem (GPS) sensor, compass, accelerometer, or other sensor. Themachine 700 may include an output controller 728, such as a serial(e.g., universal serial bus (USB), parallel, or other wired or wireless(e.g., infrared (IR), near field communication (NFC), etc.) connectionto communicate or control one or more peripheral devices (e.g., aprinter, card reader, etc.).

The storage device 716 may include a machine readable medium 722 onwhich is stored one or more sets of data structures or instructions 724(e.g., software) embodying or utilized by any one or more of thetechniques or functions described herein. The instructions 724 may alsoreside, completely or at least partially, within the main memory 704,within static memory 706, or within the hardware processor 702 duringexecution thereof by the machine 700. In an example, one or anycombination of the hardware processor 702, the main memory 704, thestatic memory 706, or the storage device 716 may constitute the machinereadable medium 722.

While the machine readable medium 722 is illustrated as a single medium,the term “machine readable medium” may include a single medium ormultiple media (e.g., a centralized or distributed database, orassociated caches and servers) configured to store the one or moreinstructions 724.

The term “machine readable medium” may include any medium that iscapable of storing, encoding, or carrying instructions for execution bythe machine 700 and that cause the machine 700 to perform any one ormore of the techniques of the present disclosure, or that is capable ofstoring, encoding or carrying data structures used by or associated withsuch instructions. Non-limiting machine readable medium examples mayinclude solid-state memories, and optical and magnetic media. In anexample, a massed machine readable medium comprises a machine-readablemedium with a plurality of particles having invariant (e.g., rest) mass.Accordingly, massed machine-readable media are not transitorypropagating signals. Specific examples of massed machine readable mediamay include: non-volatile memory such as semiconductor memory devices(e.g., Electrically Programmable Read-Only Memory (EPROM), ElectricallyErasable Programmable Read-Only Memory (EEPROM)) and flash memorydevices; magnetic disks, such as internal hard disks and removabledisks; magneto-optical disks; and CD-ROM and DVD-ROM disks.

The instructions 724 (e.g., software, programs, an operating system(OS), etc.) or other data are stored on the storage device 721, can beaccessed by the memory 704 for use by the processor 702. The memory 704(e.g., DRAM) is typically fast, but volatile, and thus a different typeof storage than the storage device 721 (e.g., an SSD), which is suitablefor long-term storage, including while in an “off” condition. Theinstructions 724 or data in use by a user or the machine 700 aretypically loaded in the memory 704 for use by the processor 702. Whenthe memory 704 is full, virtual space from the storage device 721 can beallocated to supplement the memory 704; however, because the storage 721device is typically slower than the memory 704, and write speeds aretypically at least twice as slow as read speeds, use of virtual memorycan greatly reduce user experience due to storage device latency (incontrast to the memory 704, e.g., DRAM). Further, use of the storagedevice 721 for virtual memory can greatly reduce the usable lifespan ofthe storage device 721.

In contrast to virtual memory, virtual memory compression (e.g., theLinux® kernel feature “ZRAM”) uses part of the memory as compressedblock storage to avoid paging to the storage device 721. Paging takesplace in the compressed block until it is necessary to write such datato the storage device 721. Virtual memory compression increases theusable size of memory 704, while reducing wear on the storage device721.

Storage devices optimized for mobile electronic devices, or mobilestorage, traditionally include MMC solid-state storage devices (e.g.,micro Secure Digital (microSD™) cards, etc.). MMC devices include anumber of parallel interfaces (e.g., an 8-bit parallel interface) with ahost device, and are often removable and separate components from thehost device. In contrast, eMMC™ devices are attached to a circuit boardand considered a component of the host device, with read speeds thatrival serial ATA™ (Serial AT (Advanced Technology) Attachment, or SATA)based SSD devices. However, demand for mobile device performancecontinues to increase, such as to fully enable virtual oraugmented-reality devices, utilize increasing networks speeds, etc. Inresponse to this demand, storage devices have shifted from parallel toserial communication interfaces. Universal Flash Storage (UFS) devices,including controllers and firmware, communicate with a host device usinga low-voltage differential signaling (LVDS) serial interface withdedicated read/write paths, further advancing greater read/write speeds.

The instructions 724 may further be transmitted or received over acommunications network 726 using a transmission medium via the networkinterface device 720 utilizing any one of a number of transfer protocols(e.g., frame relay, internet protocol (IP), transmission controlprotocol (TCP), user datagram protocol (UDP), hypertext transferprotocol (HTTP), etc.). Example communication networks may include alocal area network (LAN), a wide area network (WAN), a packet datanetwork (e.g., the Internet), mobile telephone networks (e.g., cellularnetworks), Plain Old Telephone (POTS) networks, and wireless datanetworks (e.g., Institute of Electrical and Electronics Engineers (IEEE)802.11 family of standards known as Wi-Fi®, IEEE 802.16 family ofstandards known as WiMax®), IEEE 802.15.4 family of standards,peer-to-peer (P2P) networks, among others. In an example the networkinterface device 720 may include one or more physical jacks (e.g.,Ethernet, coaxial, or phone jacks) or one or more antennas to connect tothe communications network 726. In an example, the network interfacedevice 720 may include a plurality of antennas to wirelessly communicateusing at least one of single-input multiple-output (SIMO),multiple-input multiple-output (MIMO), or multiple-input single-output(MISO) techniques. The term “transmission medium” shall be taken toinclude any intangible medium that is capable of storing, encoding orcarrying instructions for execution by the machine 700, and includesdigital or analog communications signals or other intangible medium tofacilitate communication of such software.

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples”. Such examples can include elements in addition tothose shown or described. However, the present inventors alsocontemplate examples in which only those elements shown or described areprovided. Moreover, the present inventors also contemplate examplesusing any combination or permutation of those elements shown ordescribed (or one or more aspects thereof), either with respect to aparticular example (or ne or more aspects thereof), or with respect toother examples (or one or more aspects thereof) shown or describedherein.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” may include “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In the appended claims, the terms “including” and“in which” are used as the plain-English equivalents of the respectiveterms “comprising” and “wherein”. Also, in the following claims, theterms “including” and “comprising” are open-ended, that is, a systemdevice, article, or process that includes elements in addition to thoselisted after such a term in a claim are still deemed to fall within thescope of that claim. Moreover, in the following claims, the terms“first,” “second,” and “third,” etc. are used merely as labels, and arenot intended to impose numerical requirements on their objects.

In various examples, the components, controllers, processors, units,engines, or tables described herein can include, among other things,physical circuitry or firmware stored on a physical device. As usedherein, “processor” means any type of computational circuit such as, butnot limited to, a microprocessor, a microcontroller, a graphicsprocessor, a digital signal processor (DSP), or any other type ofprocessor or processing circuit, including a group of processors ormulti-core devices.

The term “horizontal” as used in this document is defined as a planeparallel to the conventional plane or surface of a substrate, such asthat underlying a wafer or die, regardless of the actual orientation ofthe substrate at any point in time. The term “vertical” refers to adirection perpendicular to the horizontal as defined above.Prepositions, such as “on,” “over,” and “under” are defined with respectto the conventional plane or surface being on the top or exposed surfaceof the substrate, regardless of the orientation of the substrate; andwhile “on” is intended to suggest a direct contact of one structurerelative to another structure which it lies “on” (in the absence of anexpress indication to the contrary); the terms “over” and “under” areexpressly intended to identify a relative placement of structures (orlayers, features, etc.), which expressly includes—but is not limitedto—direct contact between the identified structures unless specificallyidentified as such. Similarly, the terms “over” and “under” are notlimited to horizontal orientations, as a structure may be “over” areferenced structure if it is, at some point in time, an outermostportion of the construction under discussion, even if such structureextends vertically relative to the referenced structure, rather than ina horizontal orientation.

The terms “wafer” and “substrate” are used herein to refer generally toany structure on which integrated circuits are formed, and also to suchstructures during various stages of integrated circuit fabrication. Thefollowing detailed description is, therefore, not to be taken in alimiting sense, and the scope of the various embodiments is defined onlyby the appended claims, along with the full scope of equivalents towhich such claims are entitled.

Various embodiments according to the present disclosure and describedherein include memory utilizing a vertical structure of memory cells(e.g., NAND strings of memory cells). As used herein directionaladjectives will be taken relative a surface of a substrate upon whichthe memory cells are formed (i.e., a vertical structure will be taken asextending away from the substrate surface, a bottom end of the verticalstructure will be taken as the end nearest the substrate surface and atop end of the vertical structure will be taken as the end farthest fromthe substrate surface).

As used herein, directional adjectives, such as horizontal, vertical,normal, parallel, perpendicular, etc., can refer to relativeorientations, and are not intended to require strict adherence tospecific geometric properties, unless otherwise noted. For example, asused herein a vertical structure need not be strictly perpendicular to asurface of a substrate but may instead be generally perpendicular to thesurface of the substrate, and may form an acute angle with the surfaceof the substrate (e.g., between 60 and 120 degrees, etc.).

In some embodiments described herein, different doping configurationsmay be applied to a source-side select gate (SGS), a control gate (CG),and a drain-side select gate (SGD), each of which, in this example, maybe formed of or at least include polysilicon, with the result such thatthese tiers (e.g., polysilicon, etc.) may have different etch rates whenexposed to an etching solution. For example, in a process of forming amonolithic pillar in a 3D semiconductor device, the SGS and the CG mayform recesses, while the SGD may remain less recessed or even notrecessed. These doping configurations may thus enable selective etchinginto the distinct tiers (e.g., SGS, CG, and SGD) in the 3D semiconductordevice by using an etching solution (e.g., tetramethylammonium hydroxide(TMCH)).

Operating a memory cell, as used herein, includes reading from, writingto, or erasing the memory cell. The operation of placing a memory cellin an intended state is referred to herein as “programming,” and caninclude both writing to or erasing from the memory cell (e.g., thememory cell may be programmed to an erased state).

According to one or more embodiments of the present disclosure, a memorycontroller (e.g., a processor, controller, firmware, etc.) locatedinternal or external to a memory device, is capable of determining(e.g., selecting, setting, adjusting, computing changing, clearing,communicating, adapting, deriving, defining, utilizing, modifying,applying, etc.) a quantity of wear cycles, or a wear state (e.g.,recording wear cycles, counting operations of the memory device as theyoccur, tracking the operations of the memory device it initiates,evaluating the memory device characteristics corresponding to a wearstate, etc.)

According to one or more embodiments of the present disclosure, a memoryaccess device may be configured to provide wear cycle information to thememory device with each memory operation. The memory device controlcircuitry (e.g., control logic) may be programmed to compensate formemory device performance changes corresponding to the wear cycleinformation. The memory device may receive the wear cycle informationand determine one or more operating parameters (e.g., a value,characteristic) in response to the wear cycle information.

It will be understood that when an element is referred to as being “on,”“connected to” or “coupled with” another element, it can be directly on,connected, or coupled with the other element or intervening elements maybe present. In contrast, when an element is referred to as being“directly on,” “directly connected to” or “directly coupled with”another element, there are no intervening elements or layers present. Iftwo elements are shown in the drawings with a line connecting them, thetwo elements can be either be coupled, or directly coupled, unlessotherwise indicated.

Method examples described herein can be machine or computer-implementedat least in part. Some examples can include a computer-readable mediumor machine-readable medium encoded with instructions operable toconfigure an electronic device to perform methods as described in theabove examples. An implementation of such methods can include code, suchas microcode, assembly language code, a higher-level language code, orthe like. Such code can include computer readable instructions forperforming various methods. The code may form portions of computerprogram products. Further, the code can be tangibly stored on one ormore volatile or non-volatile tangible computer-readable media, such asduring execution or at other times. Examples of these tangiblecomputer-readable media can include, but are not limited to, hard disks,removable magnetic disks, removable optical disks (e.g., compact discsand digital video disks), magnetic cassettes, memory cards or sticks,random access memories (RAMs), read only memories (ROMs), solid statedrives (SSDs), Universal Flash Storage (UFS) device, embedded MMC (eMMC)device, and the like.

Example 1 is a method for implementing a memory block retirement policyfor a flash memory array, the method comprising: in response toencountering a read error in a first memory block of the flash memoryarray that exceeds a first error threshold: provisionally removing thefirst memory block from service, the first memory block comprisingmultiple memory pages; copying recoverable data of the first memoryblock to a second memory block of the flash memory array; after theremoving of the first memory block from service, and the coping of therecoverable data of the first memory block to the second memory block,during each of multiple iterations: erasing the first memory block;programming the first memory block after the erasing of the first memoryblock; reading the multiple memory pages of the first memory block afterthe programming of the first memory block; and determining whether atleast one of the multiple memory pages exhibits a read error exceeding asecond error threshold during the reading of the multiple memory pages;and returning the first memory block to service in response to none ofthe multiple memory pages exhibiting a read error exceeding the seconderror threshold during the reading of the multiple memory pages duringthe multiple iterations.

In Example 2, the subject matter of Example 1 optionally includespermanently retiring the first memory block from service in response toat least one of the multiple memory pages exhibiting a read errorexceeding the second error threshold during the multiple iterations.

In Example 3, the subject matter of any one or more of Examples 1-2optionally include wherein the second memory block comprises a memoryblock from a pool of free memory blocks, and the method furthercomprises: placing the second memory block in service after the copyingof the recoverable data of the first memory block to the second memoryblock.

In Example 4, the subject matter of any one or more of Examples 1-3optionally include wherein the returning of the first memory block toservice comprises returning the first memory block to a pool of freememory blocks.

In Example 5, the subject matter of any one or more of Examples 1-4optionally include wherein the first error threshold comprises acorrectable error threshold, and the recoverable data of the firstmemory block comprises all data of the first memory block.

In Example 6, the subject matter of any one or more of Examples 1-5optionally include wherein the first error threshold comprises anuncorrectable error threshold, and the recoverable data of the firstmemory block comprises less than all data of the first memory block.

In Example 7, the subject matter of any one or more of Examples 1-6optionally include wherein the encountering of the read error in thefirst memory block occurs during a read operation employing a defaultread voltage for the control gate of each memory cell of the firstmemory block.

In Example 8, the subject matter of any one or more of Examples 1-7optionally include wherein the encountering of the read error in thefirst memory block occurs during a read operation employing a readvoltage that is offset from a default read voltage for the control gateof each memory cell of the first memory block.

In Example 9, the subject matter of any one or more of Examples 1-8optionally include wherein the reading of the multiple memory pages ofthe first memory block comprises varying a read voltage for at least oneof the multiple memory pages during an iteration of the multipleiterations.

In Example 10, the subject matter of Example 9 optionally includeswherein the varying of the read voltage is employed to increase a readwindow budget during the iteration of the multiple iterations.

In Example 11, the subject matter of any one or more of Examples 1-10optionally include receiving, from a host device, a read command to readthe first memory block; performing a read operation on the first memoryblock in response to receiving the read command, wherein theencountering of the read error occurs during the read operation.

In Example 12, the subject matter of any one or more of Examples 1-11optionally include wherein the encountering of the read error occursduring an error scrubbing process performed on the first memory block.

In Example 13, the subject matter of any one or more of Examples 1-12optionally include wherein the multiple iterations occur during one ormore periods of time during which commands from a host for access to theflash memory array are not processed.

Example 14 is a data storage system comprising: a flash memory arraycomprising multiple memory blocks, each of the multiple memory blockscomprising multiple memory pages; one or more hardware processors; and amemory storing instructions that, when executed by at least one of theone or more hardware processors, cause the data storage system toperform operations comprising: in response to encountering a read errorin a first memory block of the flash memory array that exceeds a firsterror threshold: removing the first memory block from service, the firstmemory block comprising multiple memory pages; copying recoverable dataof the first memory block to a second memory block of the flash memoryarray; after the removing of the first memory block from service, andthe coping of the recoverable data of the first memory block to thesecond memory block, during each of multiple iterations: erasing thefirst memory block; programming the first memory block after the erasingof the first memory block; reading the multiple memory pages of thefirst memory block after the programming of the first memory block; anddetermining whether at least one of the multiple memory pages exhibits aread error exceeding a second error threshold during the reading of themultiple memory pages; and returning the first memory block to servicein response to none of the multiple memory pages exhibiting a read errorexceeding the second error threshold during the reading of the multiplememory pages during the multiple iterations.

In Example 15, the subject matter of Example 14 optionally includeswherein: the first error threshold comprises an uncorrectable errorthreshold; and the encountering of the read error in the first memoryblock persists after an error handling process is performed on the firstmemory block.

In Example 16, the subject matter of any one or more of Examples 14-15optionally include wherein the reading of the multiple memory pages ofthe first memory block comprises varying a read voltage for at least oneof the multiple memory pages during an iteration of the multipleiterations.

In Example 17, the subject matter of Example 16 optionally includeswherein the reading of the multiple memory pages of the first memoryblock comprises reading each of the multiple memory pages multiple timeswhile varying the read voltage during the iteration of the multipleiterations.

In Example 18, the subject matter of any one or more of Examples 14-17optionally include wherein the flash memory array comprises amulti-level cell NAND memory array.

In Example 19, the subject matter of any one or more of Examples 14-18optionally include wherein: the flash memory array comprises athree-dimensional NAND memory array; and each of the multiple memorypages of the three-dimensional NAND memory array comprises avertically-oriented two-dimensional array of memory cells.

Example 20 is a non-transitory computer-readable data storage storinginstructions that, when executed by one or more hardware processors of adata storage system, cause the data storage system to perform operationscomprising: in response to encountering a read error in a first memoryblock of a flash memory array that exceeds a first error threshold:removing the first memory block from service, the first memory blockcomprising multiple memory pages; copying recoverable data of the firstmemory block to a second memory block of the flash memory array; afterthe removing of the first memory block from service, and the coping ofthe recoverable data of the first memory block to the second memoryblock, during each of multiple iterations: erasing the first memoryblock; programming the first memory block after the erasing of the firstmemory block; reading the multiple memory pages of the first memoryblock after the programming of the first memory block; and determiningwhether at least one of the multiple memory pages exhibits a read errorexceeding a second error threshold during the reading of the multiplememory pages; and returning the first memory block to service inresponse to none of the multiple memory pages exhibiting a read errorexceeding the second error threshold during the reading of the multiplememory pages during the multiple iterations.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. Also, in the above Detailed Description,various features may be grouped together to streamline the disclosure.This should not be interpreted as intending that an unclaimed disclosedfeature is essential to any claim. Rather, inventive subject matter maylie in less than all features of a particular disclosed embodiment.Thus, the following claims are hereby incorporated into the DetailedDescription, with each claim standing on its own as a separateembodiment, and it is contemplated that such embodiments can be combinedwith each other in various combinations or permutations. The scope ofthe invention should be determined with reference to the appendedclaims, along with the full scope of equivalents to which such claimsare entitled.

The invention claimed is:
 1. A data storage system, comprising: a flashmemory array comprising multiple memory blocks, each of the multiplememory blocks comprising multiple memory pages; one or more memorycontrollers configured to: detect read errors in a first memory block ofthe flash memory array in a first read mode; in response to the detectedread errors in the first memory block, provisionally remove the firstmemory block from service and test the first memory block in a secondread mode, the second read mode comprising a background operation mode,wherein, to test the first memory block in the second read mode, the oneor more controllers are configured to: program data to the first memoryblock at each of multiple test iterations; read memory pages of thefirst memory block at different read voltages at each of the multipletest iterations; determine a raw bit error rate (RBER) for the memorypages at the different read voltages; and determine whether to returnthe provisionally removed first memory block to service or retire thefirst memory block based on the determined RBER for the different readvoltages.
 2. The data storage system of claim 1, wherein, to test thefirst memory block in the second read mode, the one or more controllersare configured to: copy data from the first memory block to a freememory block; and erase the first memory block.
 3. The data storagesystem of claim 1, wherein the one or more memory controllers areconfigured to program different data to the first memory block for eachof the multiple test iterations.
 4. The data storage system of claim 1,wherein the one or more memory controllers comprises a memory controllerfor the data storage system and the data storage system comprising asingle memory device.
 5. The data storage system of claim 1, wherein thebackground operation mode is a mode during which commands from a hostfor access to the flash memory array are not processed.
 6. The datastorage system of claim 1, wherein the one or more memory controllersare configured to: receive, from a host device, a read command to readthe first memory block; and perform a read operation on the first memoryblock in response to a received read command, wherein the one or morecontrollers are configured to detect the read errors during the readoperation.
 7. The data storage system of claim 6, wherein the seconderror threshold comprises a correctable error threshold, at which alldetected read errors are correctable.
 8. The data storage system ofclaim 1, wherein the one or more memory controllers are configured to,in response to the detected read errors in the first memory blockexceeding the first error threshold, copy data of the first memory blockto a second memory block of the flash memory array and erase the firstmemory block before provisionally removing the first memory block fromservice.
 9. The data storage system of claim 1, wherein, to detect readerrors in the first memory block of the flash memory array in the firstread mode, the one or more memory controllers are configured to detectread errors in the first memory block that exceed a first errorthreshold, the first error threshold comprising an uncorrectable errorthreshold.
 10. The data storage system of claim 1, wherein the one ormore memory controllers are configured to determine to return theprovisionally removed first memory block to service if the determinedread errors do not exhibit a read error rate exceeding a second errorthreshold at the read voltage associated with the lowest determinedRBER.
 11. The data storage system of claim 1, wherein the multiple testiterations comprise more than two test iterations.
 12. A method forimplementing a memory block retirement policy for a flash memory array,the method comprising: detecting read errors in a first memory block ofa flash memory array in a first read mode; in response to the detectedread errors in the first memory block, provisionally removing the firstmemory block from service and testing the first memory block in a secondread mode, the second read mode comprising a background operation mode,wherein testing the first memory block in the second read modecomprises: programming data to the first memory block at each ofmultiple test iterations, reading memory pages of the first memory blockat different read voltages at each of the multiple test iterations;determining a raw bit error rate (RBER) for the memory pages at thedifferent read voltages; and determining whether to return theprovisionally removed first memory block to service or retire the firstmemory block based on the determined RBER for the different readvoltages.
 13. The method of claim 12, wherein testing the first memoryblock in the second read mode comprises: copying data from the firstmemory block to a free memory block; erasing the first memory block. 14.The method of claim 12, wherein programming data to the first memoryblock at each of the multiple test iterations comprises programmingdifferent data to the first memory block for each of the multiple testiterations.
 15. The method of claim 12, wherein the multiple testiterations comprise more than two test iterations.
 16. A non-transitorycomputer-readable data storage storing instructions that, when executedby one or more hardware processors of a data storage system, cause thedata storage system to perform operations comprising: detecting readerrors in a first memory block of a flash memory array in a first readmode; in response to the detected read errors in the first memory block,provisionally removing the first memory block from service and testingthe first memory block in a second read mode, the second read modecomprising a background operation mode, wherein testing the first memoryblock in the second read mode comprises: programming data to the firstmemory block at each of multiple test iterations; reading memory pagesof the first memory block at different read voltages at each of themultiple test iterations; determining a raw bit error rate (RBER) forthe memory pages at the different read voltages; and determining whetherto return the provisionally removed first memory block to service orretire the first memory block based on the determined RBER for thedifferent read voltages.
 17. The non-transitory computer-readable datastorage of claim 16, wherein testing the first memory block in thesecond read mode comprises: copying data from the first memory block toa free memory block; erasing the first memory block.
 18. Thenon-transitory computer-readable data storage of claim 16, whereinprogramming data to the first memory block at each of the multiple testiterations comprises programming different data to the first memoryblock for each of the multiple test iterations.
 19. The non-transitorycomputer-readable data storage of claim 16, wherein the multiple testiterations comprise more than two test iterations.